I built revell 7c using O ring type seals for control rod but I also see rubber boots are available for same function. To me O ring type demands more torque on servo and requires grease before every run. I am using Rcarb system in my type7c. Is there any reason i should avoid using rubber boots?

A number of folks use the rubber boot to seal the control rods. They are standard equipment on OTW dive modules. I also use them on my custom-built dive module for my Seehund which uses an Engel piston. The over pressure created when using the piston doesn't create any problems at all...so I would assume that the same would be true for an RCABS system.

Thank you for your reply. I am a new comer to this hobby and I saw many subs use rather complicated looking and unreliable (to novice's eye) O ring type seals. I didn't give too much thought when i chose to use engel control rod seal just because i saw.more subs were built using O ring type. Can anyone enlighten me on advantage of using O-ring type seals over rubber boots?

The cup seals take up significantly less room, which is important for smaller boats. They're likely less prone to damage from pointy tools during maintenance as well. Bellows (rubber boot) seals apply force on the servo when retracted or extended as the rubber fights to return to is formed shape. The cup seals may require more force to move (marginally), but they exert no centering force on the servo once in position. Bellows seals are more forgiving in regards to alignment. Typically servo throws change the angle of the linkage slightly, which can result in binding in the tight tolerances of the brass housings of the cup seals. Cup seals do not seal pressure well when it goes from the inside out. They work best for pressure going into the WTC, not out. They're basically uni-directional, so not good for pressure style systems like piston or pump that pressurize the dry areas.

Please note: cup seals are a different animal from o-ring seals. Cup seals have a flatter profile, similar to a washer, and are shaped much like a shallow cup, hence the name. Unlike o-rings, cup seals have very little friction with the shaft and offer far less resistance to motion. Also, the greater the external pressure, the tighter they seal. They require much less lubrication than 0-rings, and are good for both linear and rotational shaft motion. The uni-directional characteristics of cup seals can be offset by using two back-to-back. Cup seals are in very wide use in this hobby to seal both control rods and propeller shafts.

George "Crazy Ivan" Protchenko

“There are the assassins, the dealers in death; I am the Avenger!”-Nemo"I'm disinclined to acquiesce to your request; means No!"-Capt.Barbossa